Monitoring microvascular reactivity in dental subjects.

In this section of a larger study, a system for monitoring changes in the microcirculation, in humans in the dental setting, is described. The technique involves clinical nailfold capillary photomicroscopy and electronic image-scan measurements. The system was tested using reactive hyperemia after vascular occlusion; it proved reliable and sufficiently sensitive for measuring vascular reactivity in humans. (In a subsequent paper, clinical findings relative to the use of this technique with patients undergoing nitrous oxide/oxygen anesthesia will be presented).The importance of the microcirculation for the integrity of the tissues cannot be overemphasized. Since the term "microcirculation" can be defined as the microscopic subdivisions of the vascular system that lie within the tissue proper and are exposed to its immediate environment,(1) it is evident that most of the exchange of nutrients and waste products occuring in the tissue will occur at this level. Furthermore, the adequacy of tissue perfusion during drug administration, or during and after anesthesia, is dependent on the adequacy and reactivity of this subdivision of the vascular system.(2)A basic prerequisite to the understanding of microcirculatory function in a given vascular bed is the precise quantitation of dimensional changes in those vessels(3). Dynamic measurements in vivo are required, since it is difficult, if not impossible, to ensure that the dimensions obtained from fixed tissue specimens are accurate measures of those occurring in the living state. This is especially true where vessel dimensions are rapidly changing in response to endogenous or exogenous influences. Unfortunately the task of in vivo measurement of microvascular dimensions is difficult in most microcirculatory beds. Since the vessels are an integral part of a threedimensional structure,(4) the tasks of visualizing, isolating and measuring the vessels are formidable. These difficulties are compounded if the particular vessels to be studied are in human subjects where surgical intervention is unacceptable. For these reasons, previous studies of dimensional changes in the microcirculation, involving a variety of techniques (still photography, cinematography, television microscopy,(5) image-scanning,(6) image-shearing(7,8) and optical density measurements(9)), were almost always carried out in animals.In order to determine the effects of drugs and anesthetic gases on the peripheral microcirculation in human subjects undergoing dental treatment, we have employed a non-invasive photomicrographic method to measure planar dimensional changes in human nailfold capillaries. In this report we will describe this technique, its use in measuring microcirculatory changes in humans in a dental setting, and the results of a study undertaken to determine if it is sensitive enough to measure an induced change in vascular dimensions.